Control of a 3-port weld cylinder is a difficult problem which to date still has problems due to the technology used. The current technology used in the field has not been updated for approximately twenty years. It was discovered that using this current technology would not solve the current control problems inherent in a 3-port weld cylinder. Therefore, an update to the latest technology was required.
The current method of controlling a 3-port weld gun is to have a bank of manually adjusted regulators, all preset to specific pressures and mounted to solenoid valves so that when a specific valve is turned on, that particular preset pressure is applied to the weld gun. The selected pressure and the line pressure are sent to a 5-port, 2-way solenoid valve. In one position, the preset pressure is sent to the extend port of the cylinder while the return port is exhausted. In the other position, the return port is pressurized with the line pressure while the extend port is exhausted. An alternative method currently used is to have one preset pressure sent to the 5-port, 2-way solenoid valve. In one position, the preset pressure is sent to the extend port of the cylinder while the return port is exhausted. In the other position, the return port is pressurized with the preset pressure while the extend port is exhausted.
The current method only allows a discrete set of preselected pressures to be applied to the weld gun. Addition of another discrete selectable pressure requires adding another valve to the control system which can be expensive and time consuming depending on space and other factors. The larger this discrete set of pressures is made the larger, heavier, and more unwieldy the pressure control system becomes. The further a valve is from the system to be controlled the longer it takes for a change in pressure to be applied by the controlled system.